Hitherto, flexible vinyl chloride resins, ethylene-vinyl acetate resins, thermoplastic urethane resins, nylon 12, polyester elastomers have been used as materials which provide hard rubber-like or leather-like molded products.
However, flexible vinyl chloride resins, ethylene-vinyl acetate resins, thermoplastic urethane resins, nylon 12, and polyester elastomers have problems and defects in low-temperature resistance, wear resistance, processability, and hydrolysis resistance and heat aging resistance, respectively. These have been obstacles to development of practical uses.
The following proposals have been made as thermoplastic elastomer compositions prepared from polyethylene terephthalate or polybutylene terephthalate which can be industrially produced in large scale and is cheaply available.
Japanese Patent Kokai No. 63-113056 has proposed compositions of saturated polyester resin and ethylene-unsaturated epoxy compound copolymer or ethylene-unsaturated epoxy compound-ethylenically unsaturated compound copolymer.
Japanese Patent Application No. 3-88836 has proposed a composition comprising three components of saturated polyester resin, epoxy group-containing ethylene copolymer and polyfunctional compound having reactivity with epoxy group, carboxyl group and hydroxyl group.
Patent Kohyo No. 1-501713 has proposed a composition of saturated polyester resin, ethylene-acrylic acid copolymer and ethylene-glycidyl methacrylate copolymer.
Properties have been considerably improved by using such three component system, but it has been demanded to further improve balancing of low-temperature impact resistance, heat resistance, oil resistance and rigidity for industrial utilization.
The object of the present invention is to provide a thermoplastic elastomer composition which is excellent in balancing of low-temperature resistance, especially impact resistance at low temperatures and rigidity and in processability maintaining heat resistance, wear resistance and chemical resistance which are characteristics of saturated polyester resins such as polyethylene terephthalate and polybutylene terephthalate used as main starting materials.
As a result of research conducted by the inventors on polyester elastomers comprising saturated polyester resin blended with epoxy group-containing ethylene copolymer, it has been found that thermoplastic elastomers for various molded products which are excellent in heat resistance, wear resistance, and chemical resistance and balancing of rigidity and low-temperature resistance, especially low-temperature impact resistance are obtained by blending a specific polyfunctional compound and a specific elastomer.